1. Field of the Invention
The present invention relates to a three-dimensional image capturing device by which a three-dimensional shape of a measurement subject, which is to be measured, is captured by a time-of-flight measurement.
2. Description of the Related Art
A three-dimensional measurement using a three-dimensional image capturing device is classified as an active system, in which light, an electric wave or sound is radiated onto a measurement subject, and a passive system in which the light, electric wave or sound is not output. The active system comprises the time-of-flight measurement, a phase detection using a modulated light wave, a triangulation, a moire topography, and soon, and the passive system comprises a stereo vision system, and so on.
An active system device is very bulky in comparison with that of the passive system, since the device requires a laser beam output mechanism. However, the active system device is superior regarding a distance measurement resolution, a measuring time, a measuring range and soon, and thus, despite the bulkiness, the device is utilized in various fields. In a three-dimensional image capturing device, described in xe2x80x9cMeasurement Science and Technologyxe2x80x9d (S. Christie et al., vol.6, p.1301-1308, 1995), a pulse-modulation laser beam irradiates a measurement subject, and a reflected light beam, which is reflected by the measurement subject, is received by a two-dimensional CCD sensor to which an image intensifier is attached, so that an image signal, corresponding to the reflected light beam, is converted to an electric signal. ON-OFF control of the image intensifier is carried out by a gate pulse, which is synchronized with the pulse radiation of the laser beam. According to the device, since an amount of received light, based on the reflected light beam from the measurement subject, which is positioned far from the device, is less than that of received light based on a reflected light beam from a measurement subject, which is close to the measurement subject, an output corresponding to a distance between the measurement subject and the device can be obtained for each pixel of the CCD.
In a conventional three-dimensional image capturing device as described above, although various kinds of correction information should be sensed to improve accuracy of the distance measurement, a problem would occur in which the process time of the correction information for the distance measurement, becomes excessively long.
Therefore, an object of the present invention is to reduce the process time of the distance measurement in which a three-dimensional shape of a measurement subject is sensed.
According to the present invention, there is provided a three-dimensional image capturing device, comprising a light source, a first distance information sensing processor, a second distance information sensing processor and a normalized distance information calculating processor.
The light source irradiates a distance measuring light beam, which irradiates a measurement subject and is a pulsed beam. The measurement subject reflects the distance measuring light beam to generate a reflected light beam pulse. The first distance information sensing processor senses a first reflected light component (E1) for a first reflected light sensing period. The first reflected light component corresponds to a distance from the device to the measuring subject and contains a fall of the reflected light beam pulse. The second distance information sensing processor senses a second reflected light component (E2) for a second reflected light sensing period. The second reflected light component corresponds to the distance and contains a rise of the reflected light beam pulse. The length of the second reflected light sensing period is equal to that of the first reflected light sensing period. The normalized distance information calculating processor obtains a ratio (E1)/(E1+E2), which is obtained by dividing the first reflected light component (E1) by a sum of the first and second reflected light components (E1+E2), as normalized distance information that corresponds to the distance.